Sensation v. Perception • Sensation: What occurs when a stimulus activates a receptor • Hearing repeated low frequency noise • Perception: the organization of sensory info into meaningful experiences • That must be the bass line to a rap song!
Signal-Detection Theory • Signal-Detection Theory: attempts to predict our ability to detect a given stimulus, based on context and a person’s experience • Ex. radar operators need to identify difference between enemy bombers and flocks of geese • Ex. Chicken Sexers: extremely small visible difference in male/female chicks at birth, but you can be trained to detect the difference.
Threshold • Some psychologists try to find the point at which a stimulus is first noticed • For vision, put the participant in a dark room. Slowly turn up a very precise light until he/she can see it.
Threshold • Absolute threshold: weakest amount of stimulus the average person can detect • Vision: Candle 30 miles away • Hearing: Watch ticking 20 feet away • Taste: 1 teaspoon of sugar in 20 gallons of water • Smell: 1 drop of perfume in a 3-room house • Touch: Bee’s wing falling 1 cm onto your cheek • What???
Thresholds: Subliminal Stimuli • Subliminal stimuli occur below our absolute threshold for that sense. • Detection will occur less than 50% of the time. (usually far less) • Movie theatres (in the past) would flash messages to get people to the concession stand. Popcorn sales went up 58%
Threshold • Difference Threshold: smallest amount of change in a physical stimulus that can be detected half the time. • Ex. The difference in two red shirts
Sensory Adaptation • Our senses adjust to changes in our environment • Ex: Eyes adjust in a darkened movie theatre,skin receptors adjust to swimming in cold water.
Vision: How we see • Light waves enter our eyes through the pupil • The light is focused by the lens onto the back of the eye, the retina. • On the retina there are two types of receptors • Cones help us see colors, details • Rods help us see in low light • The information from the cones & rods is passed along the optic nerve to the thalamus • From there, the info is passed to the ________________ lobes
Vision: How we see • “Color-blindness” occurs with deficiency with one’s cones • Impacts males approx. 8 times as often as females. • Usually for a limited range of colors (usually greens and reds)
Vision: How we see • Depth Perception • Overlapping objects: the one “on-top” is closer • Light & Shadow: Lighter objects usually closer. • Motion Parallax: When you move your head, closer objects appear to move more • Closer objects require eyes to look in towards each other.